How can I uncomment "#" a line using python?
Yes it is possible, but not very useful. The following naive code attempts to change line 4 of its text block within Blender. The function modify takes 4 arguments.


name - the file name of the script
lineno - the line number to change (zero based)
orig - the original start of the string to change
repl - the replacement


So if you execute the script twice, the code will be commented again. The script will attempt to find its own file name in the last 2 lines. Only tested for Linux.

import bpy
import ntpath
#this is a comment
#print("Hello Blender!") # this is code

def modify(name, lineno, orig, repl):
    t = bpy.data.texts[name]
    s = t.as_string()
    l = s.splitlines()

    if l[lineno].startswith(orig):
        l[lineno] = l[lineno].replace(orig, repl, 1)
    elif l[lineno].startswith(repl):
        l[lineno] = l[lineno].replace(repl, orig, 1)

    t.from_string("\n".join(l))

head, tail = ntpath.split(__file__)
modify(tail or ntpath.basename(head),3,"#print","print")